1. Field of the Invention
The present invention relates to heat recovery systems, and in particular relates to such systems which recover the waste heat of air conditioning and refrigeration systems for purposes of heating water.
2. Description of the Prior Art
Because of the rapidly rising costs of energy, the incentives to conserve energy are increasing, both for industrial users and domestic users. Consequently there is currently considerable interest in not only eliminating energy waste by making equipment more efficient but also by recovering energy such as waste heat which according to conventional practice is usually injected into the atmosphere without recovery.
The potential for energy conservation by the recovery of waste heat in the home is substantial because of the amount of energy required to operate air conditioning equipment and hot water heating equipment, both of which are significant users of energy. For example, an air conditioning system with a water cooled condenser, while producing a ton of refrigeration or 12,000 BTUH of cooling capacity, also produces approximately 15,000 BTUH of heat which is rejected to the atmosphere. An air conditioning system with an air cooled condenser rejects about 16,000 to 17,000 BTUH for each ton or 12,000 BTUH of cooling capacity. Of this 15,000 to 17,000 BTUH of heat for each ton of capacity, 3,000 to 5,000 BTUH is relatively easy to recover at a very nominal expense. Generally, the refrigeration system is operated totally separate from the hot water system with the result that the heat removed in the condensing process of the refrigeration system is wasted, while the water in the hot water system is heated by means of an auxiliary energy source such as gas, electricity, or oil. The cost of such fuel or energy can be great particularly in situations where large amounts of hot water are required.
It is well known in the art to use some of the heat from the condensing process of a refrigeration system to produce hot water in a storage tank. Heat is reclaimed by installing a heat exchanger in the hot gas line between the compressor and the condenser of the air conditioning system. Water from the cold water supply to the water heater is circulated through the heat exchanger by means of a small circulating pump. A temperature regulating valve controls the flow of water leaving the heat exchanger and permits only water which exceeds a predetermined temperature to circulate through the heat exchanger. This basic arrangement has been used with success and is gaining widespread acceptance. There is continuing interest in improving this basic system to make it more efficient and responsive.
It may be demonstrated that a conservative estimate of the amount of heat energy which can be recovered in an air conditioning system is approximately 40% of the energy input. Therefore in a residence with a three ton air conditioner, as much as 15 to 25 gallons of hot water can be raised from 70.degree. F. to 140.degree. F. every hour the air conditioner is running. With a five ton air conditioner, as much as 25 to 40 gallons of hot water could be produced. During the hot summer months when the air conditioner is running fairly consistently, considerably more hot water will be produced than is required for the average household. Accordingly, it is desirable to provide a waste heat recovery system which can be utilized in combination with existing hot water and air conditioning equipment in which the amount of waste heat recovered is limited to the amount needed to satisfy actual hot water requirements.